Many proposals have been made in the past to slice wood, without the use of a saw.
Such a procedure would have many advantages, the most significant being the saving in wood, since no sawdust or "kerf" will be created.
Examples of such proposals are shown in Canadian Letters Patent Nos. 982032, and 1044576.
The first of such patents relates to the slicing of wood by the process of applying compressive force along the entire extent of both sides of a wood billet or workpiece, and then forcing an elongated blade through the wood in a direction transverse to the longitudinal axis of the wood, and to the direction of the compressive force.
The second patent relates to a process in which a wooden workpiece is passed between two rollers which apply compressive force to opposite sides, and simultaneously force the workpiece against a fixed blade, which progressively slices along the length of the workpiece.
The first proposal is generally speaking unsuitable for mass production techniques in a lumber mill. The second proposal appears to have numerous advantages, and appears to offer attractive possibilities.
In practice however it is found that the nature of the wood itself creates certain serious problems.
The pressure applied to the wooden workpiece is very substantial, up to about 75% of the yield point of the wood. The knife blade must be located between the "footprints" of the two pressure rollers. As a result, it is essential that the unit pressure and the total force on both sides of the wood shall be as far as possible equal and balanced so as to avoid distorting the blade.
In practice it is found that using the technique shown in the patent, it is virtually impossible to maintain equal, balanced forces on both sides of the blade. This is because it is the nature of wood to yield to a varying extent throughout due to its anatomy. Thus if the wood on one side of the blade is soft and the wood on the other side of the blade is harder than the blade will tend to be subjected to higher pressure by the hard side of the wood. The result will be that the whole workpiece with the knife blade inside it attempts to deflect towards the soft side.
Since the hardness of the wood varies along its length, the blade will attempt to flex from one position to another within the wooden workpiece as the wooden workpiece is moved along between the rollers.
Another cause of problems is the presence of surface irregularities and imperfections.
In some cases the wooden billet will have a depression or be "scant" (under size) caused by the operation of the equipment used to prepare it.
In other cases, it will have "wane" (i.e. rounded corner) caused by deformities in the tree trunk itself.
Either case can cause unequal total pressure or force to be exerted on the blade.
The end result is that at the least the slices of wood removed from the workpiece vary in thickness and shape along their length. More seriously, the blade itself frequently becomes damaged and may break.
In spite of lengthy field trials these problems have proved insuperable, and the inventions disclosed in the two patents have not achieved any commercial success.
Accordingly, the present invention has as a general objective the provision of a method, and an apparatus, for slicing wood in which compressive forces are applied from both sides across a wooden billet, and in which the wooden billet is moved on a linear axis along its length against a blade, and in which means are provided for equalizing and balancing the force on both sides of the wood, so as to respond to any variations in the wood along its length.